Silver has long been used for its antimicrobial properties. This usage predates the scientific or medical understanding of its mechanism. For example, the ancient Greeks and Romans used silver coins to maintain the purity of water. Today silver is still used for this same purpose by NASA on its space shuttles. Treatment of a variety of medical conditions using silver nitrate was implemented before 1800. A 1% silver nitrate solution is still widely used today after delivery in infants to prevent gonorrheal ophthalmia. Since at least the later part of the nineteenth century, silver has been applied in a variety of different forms to treat and prevent numerous types of bacteria related afflictions.
Other treatments, such as the application of silver foil to post surgical wounds to prevent infection survived as a medical practice into the 1980's in Europe, and silver nitrate is still used as a topical antimicrobial agent. In the 1960's the very successful burn treatment silver complex, silver sulfadiazine, shown in formula 1 below, was developed. Commercially known as Silvadene® Cream 1%, this complex has remained one of the most effective treatments for preventing infection of second and third degree burns. Silver sulfadiazine has been shown to have good antimicrobial properties against a number of gram-positive and gram-negative bacteria. It is believed that the slow release of silver at the area of the superficial wound is responsible for the process of healing. Studies on surgically wounded rats have shown the effectiveness of both silver nitrate and silver sulfadiazine to aid in the healing process. By using these common silver antimicrobial agents, inflammation and granulation of wounds were reduced, although the complete mechanism for these phenomena is not understood.
In recent years an increasing interest in the field of biodegradable polymers for their use as drug delivery systems has occurred. The majority of this research has included the biodegradable nanoparticles poly(glycolic acid) (PGA), poly(lactic acid) (PLA), and poly(lactic-co-glycolic acid) (PLGA) because they are approved by the FDA. PGA has been used in biodegradable suture materials since the 1970's.
Recent research has explored the loading of commercially available anticancer drugs, such as Paclitaxel (IUPAC name β-(benzoylamino)-α-hydroxy-6,12b-bis(acetyloxy)-12-(benzoyloxy)-2a,3,4,4a,5,6,9,10,11,12,12a,12b-dodecahydro-4,11-dihydroxy-4a,8,13,13-tetramethyl-5-oxo-7,11-methano-1H-cyclodeca(3,4)benz(1,2-b)oxet-9-ylester,(2aR-(2a-α,4-β,4a-β,6-β,9-α(α-R*,β-S*),11-α,12-α,12a-α,2b-α))-benzenepropanoic acid), into PLGA nanoparticles for drug delivery. One of the drawbacks of this drug is its hydrophobicity which leads to a slow absorption of the drug into the body. However, the loading of Paclitaxel into PLGA has lead to increased efficacy. This is due mainly to the increase in hydrophilicity of the prepared nanoparticles.
Another existing drug delivery system used for biomedical application is the polyaminophosphazenes with amino acid ester side chains. This class of compounds ultimately degrades into products that are bio-friendly, including phosphates and ammonia. The two main polyaminophosphazenes that have been used to date are poly(di(ethyl glycinato) phosphazene) (PEGP) and poly(di(ethyl alaninato) phosphazene) (PEAP).